Introduction

When considering the structures, fabrication techniques or functionality of miniaturized optics, we see that size does matter. Compared with macroscopic optics, micro-optics is generally manufactured employing different technologies, using different materials, and often relying on entirely different optical effects (Zappe 2012). An upshot of these differences is that micro-optical components and systems may often display functionalities not possible with classical, macroscopic optics. One such functionality is intrinsic tunability, and it is tunable micro-optics that is the subject of this book.

Whereas a macroscopic optical system is usually tuned by a mechanical displacement of components, in micro-optics tunability may often be realized by a controlled change in an intrinsic property of the component itself. Thus the deformation of a soft polymer surface; the change in surface tension of a liquid; or the swelling of surface layers are all mechanisms that may be employed to tune the optical characteristics of micro-optical devices (Friese et al. 2007). The very rich portfolio of effects and materials of which we may take advantage to accomplish tunability is one reason for the broad spectrum of activities in this dynamic discipline.

In this introductory overview chapter, we provide a survey of the current state-of-the art in tunable micro-optics. Using the established knowledge base in micro-optics as a point of departure (Herzig 1998, Sinziger & Jahns 2003, Zappe 2010), we will look at those micro-optical components whose optical characteristics may be tuned using novel mechanisms inapplicable to macroscopic optics.We have organized the following sections by device, allowing for different tuning mechanisms, and will consider tunable lenses; apertures and irises; filters; and diffractive optics. The chapters which follow will address many of the concepts and devices we present here in greater depth.

Microlenses

Microlenses are likely to be the optical components most researched and developed with regard to intrinsic variability (Krogmann et al. 2007, Levy & Shamai 2008, Nguyen 2010, Zeng & Jiang 2013). A wide variety of novel actuation mechanisms for tuning the focal length of microlenses is available, due in large part to the fact that unconventional materials, such as fluids and soft matter structures, may be used to fabricate lenses on the microscale. Since these are generally not useful for manufacturing macroscopic lenses, many of the tuning techniques we will consider are thus usually unique to microlenses.